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Biomedical subjects

P Mainil-Varlet

Publications and source records attributed to P Mainil-Varlet.

26 records · Page 2Linked to original sources
PubMed1997

Long-term in vivo degradation and bone reaction to various polylactides. 1. One-year results.

Injection-moulded pins from poly(L-lactide), poly(L/DL-lactide) (95/5%) were implanted in the cortex of the tibiae of sheep. The bone-implant interface was evaluated to observe whether there is any bone resorption caused by the implants. The molecular weight and crystallinity changes upon implantation were also measured. There was no net bone loss around the implants or sterile cyst formation in any of the animals implanted with polylactides up to 1 year. The new bone formed around the poly(L-lactide) and poly(L/D-lactide) pins was separated from the implants with a thin layer of connective tissue. For the implants from poly(L/DL-lactide), there was direct apposition of bone on the polymeric material. At 1 year of implantation, the implants were not completely resorbed, although the molecular weight of polylactides was reduced from 40,000-50,000 to 500-300. The crystallinity at 1 year was about 45% for poly(L/DL-lactide) and poly(L/DL-lactide) and 65% for poly(L-lactide), respectively, indicating the presence in the degraded material of thermodynamically stable crystals.

Animals↗
PubMed1997

Effect of thermal treatment on sterility, molecular and mechanical properties of various polylactides. 2. Poly(L/D-lactide) and poly(L/DL-lactide).

Pins for orthopaedic applications injection-moulded from as-supplied poly(L/D-lactide) 95/5% and poly(L/DL-lactide) 95/5%, raw as-supplied polymers or raw methanol-extracted polymers were heat-treated for a predetermined time at 135 degrees C under moisture-free argon. The sterility, molecular weight, polydispersity, mechanical properties, and crystallinity of the heat-treated samples were evaluated. All the samples heat treated under argon were sterile after 2 h exposure to heat. The heat-treated pins and raw as-supplied polymers showed a continuous decrease in molecular weight over the entire 50 h of heating, the decrease being more substantial for poly(L/D-lactide) than poly(L/DL-lactide). Raw methanol-extracted polymers showed an increase of molecular weight after 2 h of heat treatment, followed by a gradual decrease of molecular weight up to 50 h. A drop in the bending strength, an increase in the bending moduli, and no change in the shear strength was observed for polylactide pins during the first 5 h of thermal treatment. For both the polymers, there was a progressive increase in crystallinity over time of thermal treatment, and practically no change in the melting temperature.

Bone Nails↗
PubMed1997

Resorbable polymeric inserts as a means of enhancing fixation of fractures of porotic bones. I. Stability of mechanical properties and viscoelasticity of the inserts aged in vitro.

A titanium screw-poly(L-lactide) medullary insert system intended for use in the fixation of porotic bone fractures was subjected to in vitro ageing at 37 degrees C and pH = 7.4 for up to 6 months. The pull-out force of the screw from the insert and the viscoelastic properties of the insert were measured. The pull-out force did not change up to 6 months of ageing, indicating that the polymeric insert provides a good purchase for the screws. The viscoelastic properties of the insert provides of bone and did not change substantially with temperatures up to 52 degrees C. This indicates that the medullary insert would maintain its properties in vivo even if the body temperature was increased. The molecular weight of the insert at 6 months was reduced by 60%, but the molecular weight reduction did not affect the mechanical properties of the insert.

Bone Screws↗
PubMed1996

Sterility, mechanical properties, and molecular stability of polylactide internal-fixation devices treated with low-temperature plasmas.

The effect of low-temperature plasma on sterility, molecular, mechanical, and crystalline properties of poly (L-lactide), poly (L/D-lactide) and poly (L/DL-lactide) was investigated. Polymers were treated for 15 and 30 min at 100 W with nitrogen, argon, oxygen, and carbon dioxide plasma. All polymers treated with oxygen or carbon dioxide plasma were rendered sterile after 15 min of treatment. Only 70% of the samples treated under similar conditions with nitrogen or argon plasma were sterile. Extension of the exposure time to 30 min and increasing power to 200 W did not improve sterilization efficiency. Plasma sterilization, under the conditions used, caused no significant decrease or increase in overall molecular weight or polydispersity of the polylactides used. In most instances the effect of plasma sterilization was to slightly increase the overall molecular weight of the polymers studied. Treatment with argon plasma led to a more consistent increase in molecular weight than did treatment with nitrogen, oxygen, or carbon dioxide. Analysis of the surface (skin) of a poly(L-lactide) injection-molded rod following plasma sterilization indicated an increase in molecular weight as related to the interior (core) of the rod. Comparison of Mark-Houwink plots for the surface and interior of poly(L-lactide) injection-molded rods following plasma sterilization indicated an increase in chain branching for the surface relative to the interior of the rod. Generally the highly crystalline poly(L-lactide) was less susceptible to change upon plasma treatment than was the less crystalline poly(L/D-lactide) and poly(L/DL-lactide). The mechanical properties (shear strength, bending strength, and moduli) of the polylactides were not affected by plasma treatment. The overall melting temperature and the heat of melting of polylactides studied were not affected by plasma treatment. The melting temperature of the skin of the samples was about 1 degree C higher than the melting temperature of the core due to the chain orientation upon injection-molding. Plasma treatment of the polylactides reduced the melting temperature of the skin by 3 degrees C to 5 degrees C due to the crosslinking or branching at the surface layer.

Analysis of Variance↗
PubMed1996

The effect of thermal treatment on sterility, molecular and mechanical properties of various polylactides. I. Poly(L-lactide).

Resorbable pins for the treatment of osteochondral defects produced by injection-moulding from poly(L-lactide) were subjected to the action of heat at 105-150 degrees C under a low moisture and low oxygen atmosphere for a predetermined time. Standard procedures were used to evaluate the sterility, mechanical properties, molecular weight, polydisperity and crystallinity of the heat-treated samples. All of the heat-treated samples were sterile after 2 h of exposure to heat. There was an 10% increase in the shearing strength of the samples treated thermally for up to 10 h. This was attributed to the increase in overall crystallinity and crystal dimensions in the samples which enhanced the propagation of cracks formed upon testing through areas of high ductility. There was, however, a 20-35% drop in flexural strength which might result from the decreased concentration of the amorphous regions in the heat-treated implants. A 20% increase in molecular weight of the heat-treated implants was assigned to the transesterification process between the -OH and -COOH groups present initially in the polymer and/or formed due to chain scission upon exposure of the material to heat.

Biocompatible Materials↗
PubMed1993

Functional evaluation of megaprostheses replacing the proximal femur.

Between 1987 and 1991, 20 large proximal femoral replacements were performed in 19 patients (10 males and 9 females). The median age was 60 years (15 to 89 years). Four patients presented with a primary sarcoma involving the proximal femur; 15 had bone destruction secondary to metastatic disease. Twelve of the 20 had a pathological bone fracture. The average length of the proximal femoral resection was 12 cm (7 to 26 cm). Fourteen patients could be evaluated for pain and function according to the SICOT hip-evaluation score. All patients, except one with rapidly progressing local disease, were able to walk again independently using one or two crutches. Limping and a positive Trendelenburg sign were observed in all cases but two.

Activities of Daily Living↗